prevent bubbling of escape key

[koenpunt]

When the results are showing, pressing escape only hides the results, and then prevents bubbling.

Also introduced an extra method to retrieve the search input value, so that the keydown_checker can be moved to the abstract class.
This method can also be used as an additional solution for #2370, e.g.:

$('.chosen').chosen().on('chosen:no_results', function(event, data) {
  console.log(data.chosen.get_search_field_value());
});

fixes #1256
fixes #2653

[tjschuck]

My hero.

[tjschuck]

You don't need to add all of these explicit breaks here; CoffeeScript handles that.

Docs:

Switch statements in JavaScript are a bit awkward. You need to remember to break at the end of every case statement to avoid accidentally falling through to the default case. CoffeeScript prevents accidental fall-through...

Confirmed with the "Try CoffeeScript" dingus on http://coffeescript.org/ as well.

[koenpunt]

I know, but if you don't add them, CoffeeScript returns a value, and I wanted to get rid of the return true below, so for consistency I added it everywhere.

[tjschuck]

Gotcha. Fair enough.

[tjschuck]

Ditto on all of these breaks — can be safely removed.

[tjschuck]

The biggest question I had that came out of reviewing this is WTF a backstroke is, but it looks like that name was added in the initial commit 😮 by @pfiller

👍 on this one, though!